Heat transfer arrangement

ABSTRACT

A cooling arrangement for electronic components mounted in racking systems in which access to the components is gained by moving a rack with reference to its supporting structure comprises a thin-walled cooling chamber of shallow depth carried by a fixed structure and arranged to be urged against and to conform with a wall of the rack, a pressurized liquid coolant being passed through the cooling chamber in the form of a lamina flow sheet to provide efficient cooling, the chamber being urged into its conformal position by an expandable chamber which is itself expanded by the pressurized coolant. Coolant is firstly used to expand the expandable chamber and then is ducted from that chamber into the cooling chamber from which it exits for subsequent recycling.

This is a continuation-in-part (CIP) of application Ser. No. 596,155,filed Apr. 2, 1984, which was abandoned upon the filing hereof.

This invention relates to heat transfer arrangements where heat is to betransferred from one structure to another, one being detachable from theother or merely movable with reference to the other. Although havingmore general application, the invention has particular use in rackingsystems for electronic equipment in which the equipment within the unitsmay generate excessive heat, so that cooling is necessary; efficientcooling is often inconsistent with such insertion or removal. Forexample, the use of fluid seals and couplings naturally militatesagainst easy insertion and removal of the units.

British Pat. No. 1,517,650 discloses a method of cooling electronicdevices comprising the steps of removably mounting the device or circuitadjacent a heat exchanger, said heat exchanger including a flexible wallpartly defining a closed space in communication with a coolant inlet andoutlet, the flexible wall being disposed in close proximity to saiddevice or circuit, and supplying coolant to said space, the pressure ofthe coolant being in a range sufficient to cause the flexible wall tomake a heat transfer contact with said device or circuit and also topermit coolant flow to continue during and after the removal of thedevice or circuit from the heat exchanger. In this disclosure, aflexible wall formed, for example, of thin copper sheet is bowed outunder coolant pressure to contact a surface of a device to be cooled.Moreover, since the flexible wall merely bows to make heat transfercontact, there is difficulty in ensuring a sufficient contact area and apossible problem of fatigue in the periphery of the flexible wall.

British Patent Application No. 2,121,530A, which also relates to thecooling of electronic devices, discloses an urgable wall which is bodilymoved into contact with the surface of a device to be cooled, theurgable wall being carried for bodily movement with respect to a fixedstructure by means of a resilient diaphragm or bellows. It thus seeks toovercome these problems. However, in both these earlier arrangements, itis found that the heat transfer efficiency is far lower than expected.It is thus an object of the present invention to provide an improvedarrangement which is both compact and has reasonable fluid flow ratesand can cope with the high level of heat dissipation needed in advancedtechnology electronic systems whilst still having a reasonable firstcost and low maintenance requirements.

According to one aspect of the present invention an arrangement forproviding heat transfer between two relatively movable structuresincludes surface means on one structure and urgeable or movable chambermeans on the other structure, the movable chamber means having firstwall means which, in use, lies in heat transfer association with saidsurface means, second wall means in closely spaced relationship with thefirst wall means, means maintaining the spaced relationship between thetwo wall means, inlet and outlet means by which a fluid heat transfermedium can flow into and out of the movable chamber means, thearrangement being such that a thin flowing sheet of the heat transfermedium lies against the first wall means, and urging means urging saidchamber means from a position in which its first wa11 means is spacedfrom said surface means to a position in which its first wall means isin heat transfer association with said surface means.

By this arrangement a generally lamina fluid flow is provided, togetherwith a relatively high heat transfer efficiency.

The urging means may comprise an expandable chamber into which apressured fluid is admitted Conveniently, when the heat transfer mediumis suitably pressurized, it can be used to provide such expansion. Thus,when pressure is reduced or removed, the heat transfer association ofthe surface means and the first wall means is broken at leastsufficiently to allow relative movement of the two structures withoutthe necessity of disconnection or connection of ducts and the breakingor making of seals. This is particularly advantageous when the coolingmedium is a liquid rather than a gas.

Conveniently, where the heat transfer medium is used also as thepressurizing medium, then the expanding and movable chambers are in flowcommunication.

In a racking system of the type to which reference is made above, thechambers are formed in the fixed rack structure whilst the surface meansto be in heat transfer association wth the urgable chamber is formed ona drawer unit. In a further arrangement, the chambers are formed in alid or door adapted to swing from an open to a closed position withrespect to a fixed structure on which the surface means to be in heattransfer association is formed or carried.

Preferably, the means to maintain the spaced relationship between thetwo wall means of the movable chamber comprises a series of dimplesformed on the second wall means of that chamber.

Other aspects of the invention are disclosed in embodiments of theinvention now described by way of example with reference to tneaccompanying drawings in which:

FIG. 1 is a perspective view of a racking system for electroniccomponents,

FIG. 2 is a perspective view of an alternative housing system forelectronic components,

FIG. 3 is a plan view of an movable chamber, that is to say a view onArrow III of FIGS. 1 and 2,

FIG. 4 is a sectional view upon line IV--IV of FIG. 3 in an expandedcondition,

FIG. 5 is a similar view to that of FIG. 4 in a relaxed condition,

FIG. 6 is an enlarged detail view of the region in Box VI of FIGS. 4 and5,

FIG. 7 is a detailed view on Arrow VII of FIG. 6 with an outer wallremoved,

FIG. 8 is an enlarged detail view of the region in Box VIII of FIGS. 4and 5,

FIG. 9 is an enlarged detail view of the apertured region in Box IX ofFIG. 3,

FIGS. 10 and 11 are respectively diagrammatic cross-sectional views inthe plane of line X--X of FIG. 1 in a relaxed and an expanded condition,

FIGS. 12 and 13 are upper and lower sectional views and elevation,respectively, of another embodiment of the chamber wall of the presentinvention;

FIG. 14 is a perspective view along lines A--A of FIG. 12;

FIG. 15 is a prespective view along lines B--B of FIG. 12;

FIG. 16 is a prespective view of the upper end portions of the chamberwall of the present invention;

FIG. 17 is a perspective view of the corrugated members attached to theurgable wall of the present invention; and

FIG. 18 is an enlarged detailed view of the inlet-outlet tube 14-15 ofthe present invention.

A racking system for electronic equipment shown in FIG. 1, includes arack structure 1 and a plurality of drawer units 2 slidable into and outof the rack structure before and after use. The units 2 slide on guides;they require in this instance to be cooled. Formed within each uprightregion 3, 3a of the rack structure is an movable chamber 4 through whichpressurized coolant, e.g. a water, is circulated. Walls 10 of a drawerunit 2 require to be cooled and the chambers are thus urged into heattransfer contact with those walls.

In FIG. 2, a group of leadless chip carriers 5 are mounted on a base 6with their faces to be cooled lying in generally planar relationship.Hinged to the base 6 is a cover 7 having, on an inner face, a similarchamber 4 which in use will be urged against the faces of the chipcarriers 5 for cooling purposes.

Each movable chamber 4 has an outer wall 8 which faces a wall 10 of aninserted drawer unit or the faces of the leadless chip carriers shown inFIG. 2. That embodiment of FIGS. 10 and 11 has two oppositely facingchambers 4, being in an intermediate upright region 3, whilst endupright regions, such as that illustrated at 3a, have only a singlechamber 4. The arrangement of FIG. 2 has a single such chamber beingpart of a lid or door. For ease of description FIGS. 3-9 illustrate asingle chamber arrangement, although the essential features are similar.

Referring particularly to FIGS. 3-9, each urgable chamber 4 further hasan inner wall 9 spaced from, but closely adjacent, the wall 8. Each wallis formed of a plate of suitably thin heat conducting material, e.g.stainless steel foil of between 0.1 mm and 0.2 mm, say 0.15 mmthickness, selected to accommodate any uneveness in the wall 10 or thefaces of the chip carriers.

Each chamber is urged to the position of FIGS. 4 and 11 in which itswall 8 is in heat transfer association with the wall 10 or the faces ofthe chip carriers by means of coolant pressure. To achieve this, afurther chamber 11 is provided. The further chamber 11 is bounded byresilient bellows or diaphragm regions 12. The regions 12 are formed ofa similar material to the walls 8 and 9 and may conviently be integralwith the outer wall 8.

The periphery of the regions 12 is welded to a plate region of theupright 3a or the cover 7 or, alternatively, to the periphery of afurther region 12 after the manner illustrated in FIGS. 10 and 11 toprovide a fluid sealed chamber.

The inner wall 9 is welded around its periphery to the outer wall 8 toform the chamber 4. It thus separates the chamber 4 from the chamber 11.Conveniently an elongate coolant outlet duct 13 extending substantiallythe full length of the chamber 4 is formed by an extended portion of thewall 9. This is in flow communication with an outlet pipe 14 (not shownin FIGS. 10 and 11).

An inlet pipe 15 is provided to feed pressurised coolant into thechamber 11 and thus expand that chamber from the position of FIGS. 5 and10 to the position of FIGS. 4 and 11.

A series of apertures 16 in the form of slots disposed near an oppositeedge of the chamber 4 to the outlet duct 13 are formed in that wall 9which separates the chamber 4 from the chamber 11. These slots are shownin FIG. 9. A further series of slotted apertures 17 is formed betweenthe chamber 4 and the outlet duct 13. Conveniently these are formed inthe welded periphery of the wall 9 where it is continued at 18 to formthe duct 13 as shown in FIGS. 6 and 7.

Since the walls 8, 9 are of a relatively thin material, they may movetowards one another under the urging of the pressurized coolant.Therefore, means are provided to prevent this, that is to maintain twowalls of the chamber 4 substantially at a desired spacing. FIGS. 3, 4, 5and 8 illustrate one way of achieving this by providing each inner wall9 with dimpled regions 19. This arrangement allows the outer wall 8 toadapt to the contour of the adjacent wall 10 or chip carrier withoutbeing stiffened by its inner wall 9. Moreover, coolant flow is notmaterially affected.

In operation, the pressurised coolant fluid is introduced through theinlet pipe 15 to at least substantially fill and expand the chamber 11and thus effect outward bodily urging of the chamber or chambers 4 untilthey are in heat transfer association with the surfaces to be cooled.Coolant flows through the series of apertures 16 into the chamber 4 andforms a thin sheet of coolant which flows over the inner surface of thewall 8 until it exits into the outlet duct 13 via the series of slottedapertures 17. It then passes into outlet duct 13 and then into theoutlet pipe 14 without re-entering the body the coolant in the chamber11. After cooling, the coolant is recirculated in known manner.

By way of example, one embodiment of the invention has the followingcharacteristics:

Cooling contact area: 450 mm×150 mm

Cooling depth (i.e. distance between walls 8 and 9): 1.5 mm

Inlet slots (i.e. items 16): 1 mm×5 mm (10 in number)

Outlet slots (i.e. items 17): 0.5 mm×5 mm (10 in number)

Outlet duct cross section (i.e. item 13): 5 mm×10 mm

With a water coolant, a mass flow of 16 grams/second at a pressure of 14KN/m² (2 PSI) was found to provide substantially lamina flow in thechamber 4 (a Reynolds Number of 106.5) and gave a 5 mm movement of thechamber 4 between the relaxed and the expanded states of the chamber 11.The coolant removed about 200 watts of energy with a temperature ofbetween 2° and 3° Centrigrade.

The lamina flow of the sheet of coolant within the chamber 4 is, inpractice, essential to achieve the desired high heat transferefficiency.

In the further embodiment illustrated in FIGS. 12 to 18, the variouscomponents are formed of copper or beryllium copper for improved heattransfer ability. Moreover, the wall 8 is provided with means toincrease the surface area contacted by the coolant in the urgablechamber 4 and thus further improve the heat transfer ability of thearrangement. In this embodiment, said means comprise a series ofparallel channels 30 extending between the inlet 34 and outlet 35regions of the chamber 4, but other arrangements, such as fins or pins,could be used.

The channels 30 are conveniently formed by corrugated copper sheetmembers 31 soldered at their peaks 32 to the wall 8, so as to be inintimate heat transfer relationship therewith.

The length of the channels 30, that is to say the width of each coppersheet member 31 is much less than the distance between the regions ofthe inlet 34 and outlets 35 to the chamber 4. Thus a plurality of suchmembers 31 are positioned side-by-side with their channels 30 generallyparallel within the chamber 4. This arrangement allows the wall 8 toremain reasonably flexible across the length of the channels 30 whichwould otherwise act to excessively stiffen it.

As is shown in FIG. 17, in which the wa1l 9 is omitted for clarity, thechannels 30 of adjacent corrugated members 31 are not in register; thusthe flow of an element of coolant through an individual channel 30 issplit as it enters a successive channel 30.

Conveniently, one trough 33 in every ten of the corrugations or channelsis at least partially along its length soldered to the wall 9.

As is shown in FIGS. 12, 14 and 16, conveniently the depth of eachtrough 33 in the vicinity of the outlet 35 is gradually reduced towardsthe outlet. Reference 36 denotes this reduction in depth.

In the embodiment of FIGS. 12-18, the inlet region 34 to the chamber 4is formed by terminating the wall 9 short of the wall 8, the spacing ofthese walls being maintained by the presence of the corrugated members31. Similarly, the outlet region 35 from the chamber to an outlet duct37 (similar to the duct 13 of earlier Figures) is provided bydeformation of the wall 9 and by the gradually reducing depth of thecorrugations at 36.

In FIG. 18, the inlet and outlet tubes 15 and 14 respectively aresimilar and are illustrated. They communicate with the interiorsrespectively of the chamber 11 and the duct 13/37.

The tubes are of copper, belled at 38 to locate in said interiors andreinforced by an exterior washer 39. The whole is soldered together.

Suitab1e dimensions for the embodiment of FIGS. 12-18 are as follows:

Depth of corrugations (channels 30) at outlet 35=1.2 mm.

Depth of corrugations (channels 30) elsewhere=2.5 mm.

Width of corrugated sheet members 31=20.0 mm.

Gap between adjacent sheet members 31=1.0 mm.

Outlet and Inlet pipes, 14 and 15, Diameter=8.0 mm.

Width of outlet duct 37=12.0 mm.

Depth of outlet duct 37=7.0 mm.

Thickness of copper sheet components generally=0.1 mm.

Distance between crests 32 of corrugations=5.0 mm.

We claim:
 1. A cooling arrangement for electronic components mounted ina structure in which access to the components is gained by moving onepart of the structure with reference to another, for example in aracking system, the cooling arrangement being adapted to allow suchaccess without disassembly, including surface means on one part of thestructure and movable chamber means on the other part, the movablechamber means having wall means which, in use, lie in heat transferassociation with said surface means, second wall means in closely spacedrelationship with said first wall means, inlet and outlet means by whicha fluid heat transfer medium can flow into and out of the movablechamber means, the disposition of the two wall means being such that aflowing sheet of the heat transfer medium lies against the first wallmeans in use, and urging means urging said chamber means from a positionin which its first wall means are spaced from said surface means to theposition in which its first wall means are in heat transfer associationwith said surface means, said urging means comprising chamber meanshaving inlet means through which heat transfer medium is admitted toeffect expansion of said expandable chamber means, flow connection meansconnecting the inlet means to said movable chamber means, through whichthe heat transfer medium can flow from the expandable chamber means intothe movable chamber means, and outlet means for directing heat transfermedium flow from said movable chamber means without mixing flow in theexpandable chamber means.
 2. An arrangement according to claim 1,wherein the means maintaining the spaced relationship between the twowall means comprises a series of dimples formed upon the second wallmeans.
 3. An arrangement according to claim 1, wherein the flowconnection means and the outlet means each include a series of slottedapertures formed in end-to-end relationship.
 4. An arrangement accordingto claim 3, wherein said means to direct heat transfer medium flow fromthe movable chamber comprises a duct in which the series of slottedoutlet apertures are formed.
 5. An arrangement according to claim 4,suitable for use with a liquid cooling medium, wherein the movablechamber means is about 450 mm×150 mm in cooling contact area, thedistance between the first wall means and the second wall means is about1.5 mm, the slotted apertures forming the flow connection means. are 10in number and are about 1 mm×5 mm, the slotted apertures forming theflow outlet means are 10 in number and are about 0.5 mm×5 mm, and theoutlet duct is about 50 mm² in cross sectional area.
 6. A coolingarrangement according to claim 1, wherein both the first and second wallmeans are formed of metallic foil.
 7. An arrangement according to claim1 wherein channeled heat transfer means having alternate peaks andtroughs are provided within the movable chamber, the channels extendingbetween the inlet and outlet means so as not to significantly impede theflow of the coolant sheet, and means anchoring the peaks thereof inintimate heat transfer relationship with said first wall means.
 8. Anarrangement according to claim 7 wherein the channelled heat transfermeans is in at least tow portions arranged with their channels in tandemand with a spacing between adjacent channel ends such that said firstwall is not excessively stiffened.
 9. An arrangement according to claim8 wherein said portions of the channelled heat transfer means have thechannels staggered with reference to one another.
 10. An arrangementaccording to claim 7 in which the inlet and outlet means are formed byentrance and exit regions of the channels.
 11. An arrangement accordingto claim 10 in which the troughs of the channels are deformed to provideoutlet means of smaller area than the inlet means.